Methyl methacrylate compositions

ABSTRACT

Aliphatic alcohol, and high boiling point hydroxy compound additives are added to poly methyl methacrylate to improve the ultraviolet radiation resistance of the polymer. The additives may be incorporated into the poly methyl methacrylate by including the additives with the monomers prior to polymerization. Alternatively, the additives may be incorporated into the poly methylmethacrylate by addition to polymerized methyl methacrylate.

This application is a division of U.S. application Ser. No. 07/930,496,filed Aug. 17, 1992, now abandoned which is a division of U.S.application Ser. No. 07/739,027, filed Aug. 1, 1991, now abandoned whichis a division of U.S. application Ser. No. 07/577,821, filed Jul. 26,1990, now U.S. Pat. No. 5,061,747, which is a continuation of U.S.application Ser. No. 07/385,139, filed Jul. 25, 1989, now abandonedwhich is a continuation-in-part of U.S. application Ser. No. 07/276,850,filed Nov. 28, 1988 now abandoned.

FIELD OF THE INVENTION

The present invention is directed to acrylic polymer compositions whichmay be used to form plastic products which have increased resistance toultraviolet radiation and weathering. In particular, this inventionrelates to methyl methacrylate products which show improved transparencyto ultraviolet radiation.

BACKGROUND OF THE INVENTION

Ultraviolet radiation causes methyl methacrylate polymers to deteriorateafter as little as 100 hours of exposure. Ultraviolet radiation alsotends to cause methyl methacrylate polymers to "yellow" whichconcomitantly reduces the ability of the methyl methacrylate to transmitultraviolet radiation. Reduction in the ability of methyl methacrylatepolymers to transmit ultraviolet radiation is a concern of the sunbedindustry because this usually reduces the efficiency of the tanningprocess.

The art has attempted to address the degrading effects of ultravioletradiation on methyl methacrylate by incorporating light stabilizers intothese materials. For example, U.S. Pat. No. 4,550,136 adds stericallyhindered amines (HALS) such as 2,2,6,6-tetramethyl-piperidine to themethyl methacrylate monomer prior to polymerization. Although theaddition of (HALS) produces methyl methacrylate polymers with improvedresistance to ultraviolet radiation, the addition of (HALS) isexpensive.

The art has also attempted to improve the ultraviolet radiationresistance of acrylics by addition of propyl alcohol. As discussed inthe article by A. S. Belichenkol et al, entitled "On the Mechanism ofPolymer Destruction under UV and Gamma Irradiation: The Influence of LowMolecular Weight Additives Related to Vibrational Cross-Relaxation",Sixth Symposium on Radiation Chemistry, (1986), pages 535-538, polymersamples were prepared by bulk radical polymerization of monomercompositions of methyl methacrylate which incorporate about 5-20% propylalcohol. The resultant polymers showed improved resistance toultraviolet radiation for short exposures of about 100 hours. The largeamounts of more than 5% propyl alcohol, however, would be expected todegrade the physical and mechanical properties of these polymers.

A need therefore exists to provide polymerized methyl methacrylatecompositions which may be inexpensively manufactured and which showimproved resistance to prolonged exposures to ultraviolet radiationwithout the need for addition of large amounts of additives.

SUMMARY OF THE INVENTION

The invention is directed to polymeric methacrylates which show improvedresistance to prolonged exposure to ultraviolet radiation. The mixturesof monomers which are used to form the polymeric methacrylates include aBase Mix of monomers of alkyl methacrylates such as methyl methacrylateand an alkyl acrylate which has one to four carbons in the alkyl group.Alcohols, high boiling point hydroxy compounds, and mixtures thereof maybe added to the Base Mix of monomers prior to polymerization.Alternatively, the alcohol, high boiling point hydroxy compounds, andmixtures thereof may be added to the polymerized Base Mix. The highboiling point hydroxy compounds either may be substituted for thealcohol additives or combined with the alcohol additives. Chain transferagents for controlling the molecular weight of the resultant polymeralso may be added to the Base Mix of monomers.

The compositions of the invention can be formed into sheet products andcomplex shaped articles which show surprisingly improved resistance toultraviolet radiation. The polymeric compositions may also be formedinto molding materials for use in, for example, the manufacture of meltcalendered sheet products and complex molded articles.

DETAILED DESCRIPTION OF THE INVENTION

Having summarized the invention, the invention will now be discussed indetail by reference to the following specification and non-limitingexamples.

In accordance with one aspect of the invention, hereinafter referred toas "pre-addition", aliphatic alcohols, high boiling point hydroxycompounds or combinations thereof, as well as additional additives suchas chain transfer agents, can be admixed with a Base Mix of monomers ofalkyl methacrylate and alkyl acrylate. Preferably, the alkylmethacrylate is methyl methacrylate (MMA) and, the alkyl acrylate ispreferably ethyl acrylate(EA). Other alkyl acrylates such as butylacrylate and methyl acrylate also may be employed with (MMA). (MMA) mayconstitute from about 90 to about 100 percent of the Base Mix.Correspondingly, up to about 10% alkyl acrylate may be included in theBase Mix. Preferably, the Base Mix of monomers include about 96% methylmethacrylate and about 4% ethyl acrylate.

In pre-addition, about 0.5 to 2.0% of an aliphatic alcohol is added tothe Base Mix. Preferably, aliphatic primary or secondary alcohols whichhave 1-10 carbons are added to the Base Mix. Most preferably, methyl andethyl alcohols are added to the Base Mix. As an alternative embodiment,mixtures of aliphatic alcohols may be added to the Base Mix composition.As a further alternative embodiment, high boiling point hydroxycompounds such as ethylene glycol and glycerin may be substituted for orcombined with the aliphatic alcohol. Amounts of additives outside of therange of one-half to two percent may be added to the Base Mix providedthat the amount of additive does not degrade the physical properties ofthe resultant alkyl methacrylate polymeric product. Additionally, achain transfer agent, such as about 0.5% of n-dodecylmercaptan("n-DDM")may be added to the Base Mix to control the molecular weight of theresultant polymeric material. Preferably, the amount of the chaintransfer agent added to the Base Mix composition is sufficient toproduce a polymeric material with a molecular weight of 100,000-500,000.

After the additives have been added to the Base Mix of monomers, theresultant composition may be formed into, for example, polymerized sheetproducts, by for example, standard cell casting techniques. Othertechniques, such as emulsion polymerization and suspensionpolymerization also may be employed to provide polymerized products.

PRE-ADDITION: GENERAL PROCEDURE: EXAMPLES 1-12

In accordance with the pre-addition aspect of the invention, a Base Mixof monomers of (MMA) and an alkyl acrylate such as ethyl acrylate (EA)is prepared. Alcohol additives which have 1-10 carbons, or high boilingpoint hydroxy compounds such as butyl lactate, ethylene glycol orglycerin, are added to the Base Mix. Cell cast sheet products may beformed by agitating and pouring the mixtures of monomers and additivesinto a sealed mold. The mixture is heated to about 45-120C. tosubstantially completely polymerize the Base Mix to provide cell castsheet products of polymerized methyl methacrylate polymer (PMMA).

The effects of the alcohol additives and high boiling point hydroxycompounds on the ultraviolet radiation resistance of the (PMMA) productsproduced in accordance with pre-addition were determined by subjectingthe (PMMA) products to prolonged exposures of ultraviolet radiation overthe wavelength range of 290-400 nanometers(NM) in accordance with ASTMstandard G-53-84. Samples, measuring about 0.170 inches in thickness,were exposed to 290-320 (NM) ("UVB") radiation from a PhillipsCorporation FS40 fluorescent lamp having a peak emission at 314 (NM) anda 1% of peak emission cutoff at 284 (NM). Additional samples of these(PMMA) products were exposed to the range of 315-400 (NM) ("UVA")radiation from a Q-Panel Corporation UVA-351 lamp having a peak emissionat 314 (Nm) and a 1% peak emission cutoff at 284 (NM).

The radiation resistance of the (PMMA) products was evaluated bycomparing, by means of a spectrophotometer, the percent totalultraviolet transmittance at wavelengths of 300 (NM) and 340 (NM)through the (PMMA) products both before and after exposure of the (PMMA)products to (UVA) and (UVB) radiation.

In addition to evaluating the ultraviolet radiation resistance of thesecompositions on the basis of the percent total transmittance of 300 and340 (NM) radiation, the effects of the alcohol additives and highboiling point hydroxy compounds on the extent of yellowing of (PMMA)compositions produced by pre-addition was also measured. The extent ofyellowing was measured by comparing the yellow color in the (PMMA)product after exposure to either (UVA) and (UVB) radiation with theyellow color in the (PMMA) product prior to exposure to either the (UVA)or (UVB) radiation. The result, referred to as the yellowness index(YI), was evaluated according to ASTM test method D1925. The effects ofthe pre-addition of aliphatic alcohol additives and high boiling pointhydroxy compounds on the ultraviolet radiation resistance of cell cast(PMMA) products produced by pre-addition are shown in Table I.

Examples 1-12 of Table I illustrate the effects of pre-addition ofalcohol and high boiling point hydroxy additives on the ultravioletradiation resistance of (PMMA) products formed from a Base Mix of (MMA)and (EA). As shown in Table I, (PMMA) products which employ the alcohol,and high boiling point hydroxy additives retain an extremely highpercentage of their transparency at 300 NM after 6000 hours of exposureto (UVA) radiation. As shown in Example 3, (PMMA) that includes (EA) hasa transmittance of 300 (NM) radiation of 84.3 percent. The percent totaltransmittance at 300 (NM) of the composition of Example 3, afterexposure to (UVA) radiation for 6000 hours, is 76.9%. Comparing thepercent transmittance of 300 NM radiation after 6000 hours of exposureto (UVA) radiation with the material's original transmittance of 84.3%at 3007 NM shows that composition of Example 3 retains about 91.7% ofthe transmittance of the unexposed (PMMA) composition of Example 3.However, as shown in example 1, (PMMA) which does not employ anyadditives only retains about 40% of the transmittance at 300 (NM) of theunexposed (PMMA) product of Example 1.

                                      TABLE I                                     __________________________________________________________________________                           UNEXPOSED MATERIAL                                                            % Total % Total                                                               Transmittance                                                                         Transmittance                                  Composition of Cell Cast (PMMA)                                                                      of 300 (NM)                                                                           of 340 (NM)                                                                           (Y1)                                   __________________________________________________________________________     1. Base Mix           82.4    86.0    0.8                                     2. Base Mix + 1% CH.sub.3 OH                                                                        85.0    86.8    0.8                                     3. Base Mix + 0.5% C.sub.2 H.sub.5 OH                                                               84.3    86.6    0.8                                     4. Base Mix + 1% C.sub.2 H.sub.5 OH                                                                 84.6    87.1    0.8                                     5. Base Mix + 2% C.sub.2 H.sub.4 (OH).sub.2                                                         84.5    87.3    0.8                                     6. Base Mix + 0.5% C.sub.2 H.sub.4 (OH).sub.2                                                       83.3    86.4    0.8                                     7. Base Mix + 1% C.sub.2 H.sub.4 (OH).sub.2                                                         79.7    86.4    0.8                                     8. Base Mix + 1.0% C.sub.4 H.sub.9 OH                                                               85.6    89.9    0.8                                     9. Base Mix + 1% C.sub.6 H.sub.13 OH                                                                85.3    89.5    0.8                                    10. Base Mix + 1% C.sub.10 H.sub.21 OH                                                               85.5    89.6    0.8                                    11. Base Mix + 0.33% n-DDM + 1% C.sub.2 H.sub.5 OH                                                   80.5    86.4    0.7                                    12. Base Mix +  0.33% N-DDM + 1% C.sub.2 H.sub.5 OH                                                  81.2    86.1    0.7                                    __________________________________________________________________________                           6000 Hours-(UVA) Expopsure                                                    % Total % Total                                                               Transmittance                                                                         Transmittance                                  Composition of Cell Cast (PMMA)                                                                      of 300 (NM)                                                                           of 340 (NM)                                                                           Y1)                                    __________________________________________________________________________     1. Base Mix           42.6    78.0    2.7                                     2. Base Mix + 1% CH.sub.3 OH                                                                        78.8    89.3    0.7                                     3. Base Mix + 0.5% C.sub.2 H.sub.5 OH                                                               76.9    88.5    0.8                                     4. Base Mix + 1% C.sub.2 H.sub.5 OH                                                                 83.4    89.9    0.7                                     5. Base Mix + 2% C.sub.2 H.sub.4 (OH).sub.2                                                         85.1    89.9    0.7                                     6. Base Mix + 0.5% C.sub.2 H.sub.4 (OH).sub.2                                                       68.8    87.2    1.0                                     7. Base Mix + 1% C.sub.2 H.sub.4 (OH).sub.2                                                         78.1    89.1    0.8                                     8. Base Mix + 1.0% C.sub.4 H.sub.9 OH                                                               63.5    84.9    1.5                                     9. Base Mix + 1% C.sub.6 H.sub.13 OH                                                                48.6    80.4    2.4                                    10. Base Mix + 1% C.sub.10 H.sub.21 OH                                                               46.9    78.6    2.7                                    11. Base Mix + 0.33% n-DDM + 1% C.sub. 2 H.sub.5 OH                                                  82.4    89.4    0.8                                    12. Base Mix + 0.33% N-DDM + 1% C.sub.2 H.sub.5 OH                                                   79.1    88.5    0.8                                    __________________________________________________________________________                           6000 Hours - (UVB) Exposure                                                   % Total % Total                                                               Transmittance                                                                         Transmittance                                  Composition of Cell Cast (PMMA)                                                                      of 300 (NM)                                                                           of 340 (NM)                                                                           (Y1)                                   __________________________________________________________________________     1. Base Mix           32.7    50.2    7.2                                     2. Base Mix + 1% CH.sub.3 OH                                                                        82.4    85.7    0.9                                     3. Base Mix + 0.5% C.sub.2 H.sub.5 OH                                                               76.2    83.3    1.5                                     4. Base Mix + 1% C.sub.2 H.sub.5 OH                                                                 82.9    87.6    1.0                                     5. Base Mix + 2% C.sub.2 H.sub.4 (OH).sub.2                                                         85.7    89.4    0.8                                     6. Base Mix + 0.5% C.sub.2 H.sub.4 (OH).sub.2                                                       72.0    80.7    2.0                                     7. Base Mix + 1% C.sub.2 H.sub.4 (OH).sub.2                                                         81.4    86.8    1.0                                     8. Base Mix + 1.0% C.sub.4 H.sub.9 OH                                         9. Base Mix + 1% C.sub.6 H.sub.13 OH                                         10. Base Mix + 1% C.sub.10 H.sub.21 OH                                        11. Base Mix + 0.33% n-DDM + 1% C.sub.2 H.sub.5 OH                                                   74.6    81.9    0.8                                    12. Base Mix + 0.33% N-DDM + 1% C.sub.2 H.sub.5 OH                                                   66.6    76.3    0.8                                    __________________________________________________________________________     BASE MIX = 96% METHYL METHACRYLATE, 4% ETHYL ACRYLATE                    

                  TABLE II                                                        ______________________________________                                        % Transmittance at                                                            300 NM after          % Transmittance at                                      exposure to (UVA) for 300 NM after                                                                 1000     exposure to (UVB) for                           Example                                                                              Additive 0 Hours  Hours  0 Hours                                                                              1000 Hours                             ______________________________________                                        13.    none     61.7     45.6   61.5   32.5                                   14.    1% EG.sup.1                                                                            60.6     53.2   59.7   46.7                                   15.    1% DG.sup.2                                                                            65.8     52.1   65.5   51.0                                   16.    1% GL.sup.3                                                                            66.0     51.5   65.3   47.3                                   17.    1% BL.sup.4                                                                            68.8     63.3   67.7   57.9                                   ______________________________________                                         .sup.1 EG = ethylene glycol                                                   .sup.2 DG = diethylene glycol                                                 .sup.3 GL = glycerin                                                          .sup.4 BL = butyl lactate                                                

Pre-addition also may be employed to produce resin molding materials of(PMMA) for use in the manufacture of injection molded components andmelt calendered sheets. For example, (PMMA) sheet materials can becrushed into particles and extruded to provide pellets of molding resinmaterials. Alternatively, the Base Mix of monomers may be formed intomolding resin materials by techniques such as emulsion polymerizationand suspension polymerization.

As an alternative to pre-addition, alcohol, and high boiling pointhydroxy compound additives may be incorporated into (PMMA) by directlytreating the (PMMA) with the additives. This technique, hereinafterreferred to as "post-addition", is particularly suitable for providingmaterials for molding and extrusion into complex articles such as coversfor high intensity discharge lamps.

A variety of methods may be used to achieve post-addition of the alcoholadditives into (PMMA). For example, the additives may be added directlyto the liquid polymer. The additives also can be incorporated into thepolymer by treating the surface of the polymer with the additives atroom temperature and thereafter melting the treated polymer.Post-addition may be performed at temperatures in the range of ambienttemperature to about 300 C. Where the additives are applied to liquid(PMMA), high boiling point additives are preferred in order to minimizevolatilization of the additive. High boiling point additives which maybe employed preferably include aliphatic alcohols which have 4 to 16carbons. High boiling point additives which are especially preferred foradding to liquid (PMMA) include ethylene glycol, diethylene glycol,butyl lactate and glycerin.

In examples 13 to 17 shown in Table II, (PMMA) is formed by heating amixture of about 95% methyl methacrylate(MMA), about 4% ethylacrylate(EA), about 0.20 % n-dodecyl mercaptan(n-DDM) as a chaintransfer agent to provide a molecular weight of 100,000 to 500,000 withabout 0.02% of a peroxide such as di-tert-butyl peroxide as apolymerization catalyst. The mixture is heated to a temperature and fora time sufficient to cause at least fifty percent converstion topolymer. Preferably, the additives are applied after substantially allof the residual monomers have been removed from the polymer. Thereafter,the residual monomers may be removed prior to "post-addition" of theadditives. The additive is applied to the liquid polymer just prior tosolidification. Preferably, the additives are applied while the liquidpolymer is at a temperature in the range of about 200° C. to about 250°C. Alternatively, the additives may be post-added to the (PMMA) byapplying the additives to the (PMMA) at ambient temperature. Thereafter,the treated (PMMA) is heated to above its glass transition temperature,preferably with agitation, to incorporate the additive into polymer.

The effects of the alcohol additives and high boiling point hydroxycompounds on the ultraviolet radiation resistance of the (PMMA) productsproduced by post-addition were determined by subjecting the (PMMA)products to prolonged exposures of ultraviolet radiation over thewavelength range of 290-400 nanometers(NM) in accordance with ASTMstandard G-53-84. Samples of about 0.170 inches thickness were exposedto 290-320 (NM) ("UVB") radiation from a Phillips Corporation FS40fluorescent lamp having a peak emission at 314 (NM) and a 1% of peakemission cutoff at 284 (NM). Additional samples of these (PMMA) productswere exposed to the range of 315-400 (NM) ("UVA") radiation from aQ-Panel Corporation UVA-351 lamp having a peak emission at 314 (NM) anda 1% peak emission cutoff at 284 (NM).

The radiation resistance of the (PMMA) products formed by post-additionwas evaluated by comparing, by means of a spectrophotometer, the percenttotal ultraviolet transmittance at wavelengths of 300 (NM) and 340 (NM)through the (PMMA) products both before and after exposure of the (PMMA)products to (UVA) and (UVB) radiation.

The polymeric materials formed by post-addition, as shown in Table II,also retain a surprisingly high transmittance after exposure toultraviolet radiation. As shown in Example 14 of Table II, post-additionof one percent of ethylene glycol to (PMMA) provides a material whichhas an original transmittance to 300 NM (UVA) of 60.6%. This materialretains a transmittance to 300 NM (UVA) of 53.2% after 1000 hoursexposure to 300NM (UVA). The composition of Example 14 therefore retainsa surprisingly large 87.78% of its original transmittance to 300 NM(UVA) radiation. In contrast, example 13 which does not employ anyadditives, only retains about 73.9% of the original transmittance at300NM.

While the invention has been described and exemplified in great detail,various modifications, alternative embodiments, alterations andimprovements should become apparent without departure from the spiritand scope of the invention.

We claim:
 1. A polymeric composition in the form of a molded object,extruded sheet, or cast sheet, consisting essentially of:a) a polymercomprising predominantly units of methyl methacrylate and b) from aboutone-half to about two percent by weight, of at least one alcohol, thealcohol containing no more than ten carbon atoms, wherein the at leastone alcohol is admixed with the polymer subsequent to its preparation.2. The composition of claim 1 wherein the alcohol is a monohydricaliphatic alcohol or a polyhydric aliphatic alcohol.
 3. The compositionof claim 2 wherein the monohydric aliphatic alcohol is methyl alcohol orethyl alcohol.
 4. The composition of claim 2 wherein the polyhydricaliphatic alcohol is ethylene glycol, diethylene glycol, or glycerin. 5.The composition of claim 1 wherein the alcohol is butyl lactate.
 6. Thecomposition of claim 1 wherein the polymer further contains units of analkyl acrylate.
 7. The composition of claim 6 wherein the alkyl acrylateis ethyl acrylate, butyl acrylate, or methyl acrylate.
 8. Thecomposition of claim 7 wherein the alkyl acrylate is ethyl acrylate andthe units of ethyl acrylate are about four percent of the total polymerunits.
 9. The composition of claim 1 wherein the weight-averagemolecular weight of the polymer is from about 100,000 to about 500,000and the polymeric composition is in the form of a molded object or anextruded sheet.